Testing system



H. FLETCHER TESTING SYSTEM 'May '20 1924. 1,494,349

Filed Oct. 19, 1922 Q I A g 5: a fiyz i ll] If l9 6 5 Q 6 1 M 3 a??? 2 I 1 3D uL 9 /J 50 '70 9.0 no I30 450 no arms UZI-RESHANCE V g i?) f 0 r" Haw? f'I efcher W 2% AW Patented May 2@, W24.

UNETED STATES Ltttfitd FATENT @FFlQE.

HARVEY FLETCHER, OF NEW YOUR-K, N. Y., ASSIG-INQB T 'WESTERN ELECTRIC- COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

rnsrrnssYs'rnMf I Application filed October 19, 1922. Serial no. 595,504.

To all whom it may concern:

Be it known that I, HARVEY F ETCHER, a citizen of the United States, residing at New York, in the county of New York,

State of New York, have invented certain new and useful Improvements in Testing Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to systems for de- 10 termining the efiiciency of telephone apparatus and particularly to a system for determining the efiiciency of subscribers telephone receivers.

The object of this invention in general is to provide a convenient and efiicient system for readily determining the efficiency of a subscribers receiver.

In accordance with the general features of this invention, a measure of the efiiciency of a subscribers telephone receiver is obtained by determining the ratio of the alternating current voltages which must be applied to a standard receiver and the subscribers receiver. respectively, in order that both receivers give the same output. The

standard receiver is acoustically coupled to the subscribers transmitter and is energized by a predetermined standard amount of alternating current, which causes the receiver to produce a standard output and subject the transmitter to a standard amount of agitation. This auses the transmitter to undergo a definite change in resistance, which shows that the alternating voltage generated by the transmitter has a definite value. as is well understood in the art. The subscribers receiver is then substituted for the standard receiver and the alternating current which energizes the receiver is adjusted until the output of the subscribers receiver is the same as the output of the standard receiver had been. This adjustment is determined by noting when the agitated transmitter has the same resistance in the two cases. The ratio of the voltages applied to the standard receiver and the subscribers receiver respectively, gives a measure of the efiiciency of the subscribers receiver from a telephone standpoint. This used in making the test. w

, ratio may be converted into miles of stand Fig. 2 shows characteristic curves, giving the relation between the direct current resistance of a certain type of carbon transmitter and the alternating voltage generated by the transmitter when it is subjected to various degrees of agitation.

In order to make a test, twomen are required, one to make the circuit changes and adjustments'at the central office, and the other to make them at the subscribers station. Resistance 1. which has a value equal to the resistance of a subscribers transmitter when subjected to standard agitation, is substituted for the transmitter. Resistance 2 is adjusted until meter A, shows that a direct current of the desired value. e. g. 90 milliamperes, is flowing from battery 3 through winding 4, line conductor'5, resistance 1. choke coil 12, line conductor 6 and winding 7. Resistance 1 is then replaced by transmitter T. If desired, the substitution of resistance 1 for transmitter T and vice versa, may be accomplished by means of a switch 8.

Resistance 9 is adjusted until the alternating current voltmeter V shows that voltage of a desired standard'value. e. g. 10 4 volts, is being applied to the line by generator 10, which preferably is a band frequency generator that delivers current having an energy frequency spectrum similar to voice current. The alternating current is transmitted over the subscribers loop and energizes a standard receiver R, which is placed in bridge with the line by means of a transformer comprising primary winding 13, and secondary winding 14:. It is preferable that this transformer have an impedance lookinginto winding 13, which is so high compared to the impedance of the loop that a definite voltage as indicated by voltmeter V will always cause receiver R, to give the same sound output regardless of the length of the subscribers loop. A chokecoil 12 keeps the above-mentioned alternating current from passing through the transmitter and condenser 18. The standard receiver which is now giving a definite stand ard output, is acoustically coupled to the transmitter. If desired, a tube 15 may be used to enclose an air column between the transmitter and the receiver.

' The agitation of the transmitter causes an increase in its resistance and hence a corresponding decrease in the deflection of meter A which measures the direct current supplied to the transmitter by battery 3. The change in deflection of meter A, is a function of the increase in resistance of transmitter T, which in turn is a function of the alternating voltage generated by the transmitter, as is shown by the curves of Fig. 2. For the example chosen, curve I) is the one of interest as it shows the relation between the alternating voltage generated by the transmitter and the effective direct current resistance of the transmitter for the case where the steady state direct current through the transmitter is 90 milliamperes. The alternating'voltage generated by the transmitter is a function of the output of receiver it,- and hence the change in deflection of meter A, is a measure of the output of receiver 3,. The subscribers receiver R, can now be substituted for the standard receiver R, and if meter A, indicates the same change in deflection uponagitation of the transmitter T by receiver R, as it did upon agitation of the transmitter by receiver R it is apparent that two receivers give the same output. 7

After the subscribers receiver R, has been substituted for the standard receiver 13,, resistance 9 is adjusted until the output of the receiver R, is the same as the output of receiver R, had been. The reading of voltmeter V is then noted and the ratio of the readings of voltmeter V for equal outputs by the standard receiver and the subscribers receiver, respectively, gives a measure of the efficiency of the subscribers receiver in terms of the performanceof'the standard receiver. This ratio may be converted into miles of standard cable or other convenient transmission unit.

Meter A, must have a relatively high range, which for the example chosen, would mean a full scale deflection of at least 90 milliamperes. The decrease in the direct current caused by the agitation of the transmitter may be so small that it can not be sufliciently' accurately noted on a meter of such high range. To obtainmore accurate readings, a second meter A, of lower full scale deflection, e. g. 15 milliamperes, may be inserted in series with meter A, and a battery 16 in series with a resistance 17, used to set meter A, back so that it will be operable to indicate changes in a current of the order of 90 milliamperes. The change in deflection of meter A, upon agitation of the transmitter may therefore be used as a measure of the output of the receivers.

It is seen that a method and apparatus have been provided whereby the efficiency of a subscribers receiver can'be readily determined without the receiver being removed from the subscribers station or a ground return being used between the subscribers sta tion and the central ofiice.

In the specification, mention has been made of values of current and voltage, but it is to be understood that these values are merely illustrative, and that values of voltage, current, and resistance should be chosen which are the most suitable forthe apparatus involved.

The invention claimed is:

1. A method of determining the efiiciency of a subscribers receiver which. comprises connecting a standard receiver and the subscribers receiver, one after the other, to the subscribers end of a line, applying voltage to the central ofiice end of said line, obtaining a measure of the output of each receiver, adjusting said voltage until a value is obtained for each receiver which causes that receiver t give a definite output. and comparing the two values of voltage obtained.

2. A method of determining the etliciency of a subscribers receiver which comprises connecting a standard receiver and thesubscribers receiver, one after the other, to the subscribers end of a line, energizing said receivers by applying voltage at another point in said line, adjusting said voltage until a value is obtained for each receiver which causes that receiver to give a definite output, and comparing the two values of voltage obtained.

3. A method of determining the eiliciency of a subscribers receiver which comprises connecting a standard receiver and the subscribers receiver, one after the other, in bridge of the subscribers end of a line, energizing said receivers by connecting a source of multi-frequency voltage in bridge of the central ofice end of the line, adj usting said voltage until a value is obtained for each receiver which causes that receiver to give a definite output, and comparing the two values of voltage obtained.

4:. A method of determining the efficiency of a subscribers receiver which comprises connecting a standard receiver and the subscribers receiver, one after the other, to the subscribers end of a line; energizing said receivers by connecting to the central ofiice end of the line, a source of voltage which has a frequency amplitude characteristic approximating that of speech; adjusting said voltage until a value is obtained for each receiver which causes that receiver to give a definite'output; and comparing the two values of voltage obtained.

5. A method of determining the efficiency of a subscribers receiver which comprises connecting a'standard receiver in bridge of the 'subscribers end of a line and acoustically coupling ,it to a transmitter, energizing said receiver by connecting a source of voltage in bridge of the central oflice' end of the line, relatively determining the output of said receiver by measur'ng the effective change in the direct current resistance, of saidrtransmitter, adjusting said voltage until a value is obtained which causes said receiver to produce a definite output, carrying out the foregoing process with the subscribers receiver substituted for said standard receiver and comparing the two values of voltage obtained.

6. The method of determining the efficiency of a subscribers receiver which comprises connecting a standard receiver and a transmitter in bridge of the subscribers end of a line, acoustically coupling said receiver to said transmitter, energizing said receiver by connecting a source of voltage in bridge of the central office end of'the line, relatively determining the output of said receiver by measuring the eflective change in the direct current resistance of said transmitter, adjusting said voltage until a value is obtained which causes said receiver to produce a definite output, carrying out the foregoing process with the subscribers receiver, substituting for said standard receiver, and comparing the values of voltage obtained.

7. In a system for measuring the efliciency of a telephone receiver, a transmission line, a transmitter and a standard receiver in bridge of said transmission line, means for sending direct current over the line to said transmitter, means for sending alternating current over the line to energize said receiver, means for measuring the voltage which causes said alternating current to flow, and means for substituting the receiver to be tested for said standard receiver.

8. In a system for measuring the efliciency of a telephone receiver, a transmission line, a transmitter and a standard receiver in bridge of said transmission line, means for sending direct current over the line to said transmitter, means for sending alternating current over the line to energize said receiver, means for measurin the alternating voltage which causes said a terating current to flow, means for substantially excluding said alternating current from said transmitter, and means for substituting the receiver to be tested for said standard receiver.

9. In a system for measuring the efficiency of a telephone receiver, a transmission line, a transmitter and a standard receiver in bridge of said transmission line, means for sending direct current over the line to said transmitter, means for sending alternating current over the line to energize said receiver, said alternating current having an energy frequency spectrum corresponding approximately to voice current, means for measuring the voltage which causes said alternating current to flow, and means for substituting the receiver to be tested for said standard receiver.

10. In a system for measuring the emciency of a telephone receiver, a transmission line, a transmitter and a standard re ceiver in bridge of said transmission line, means for sending direct current over the line to said transmitter, means for sending alternating current over the line to energize said receiver, means for measuring the voltage which causes said alternating current to flow, means responsive to changes in the direct current through said transmitter, and means for substituting the receiver to be tested for said standard receiver.

11. In a system for measuring the efiiciency of a telephone receiver, a transmission line, a transmitter and a standard receiver in bridge of said transmission line, means for sending direct current over the line to said transmitter, means for sending alternating current over the line to energize said receiver, means for measuring the voltage which causes said alternating current to flow, means for substantially excluding said alternating current from said transmitter, means responsive to changes in the direct current through the said transmitter, and means for substituting the receiver to be tested for said standard receiver.

In witness whereof, I hereunto subscribe my name this 17th day of October, A. D.

HARVEY FLETCHER. 

